Multi-lingual translation dictionaries are commercially available as hard copy books. Hand-held computerized translators for two languages are also commercially available. The latter is typically implemented with a database containing each word of a first language and its synonym in the second language. Various schemes have been devised for such translators to reduce memory requirements as well as searching time of the databases employed.
Attempts to extend the dictionary to include three, four or more languages, or to include, in addition to words, phrases--since certain language concepts are in the form of, or can only be translated into, a sequence or string of words--have encountered major problems and only limited success. These problems mainly involve the requirement of extremely large databases and/or requiring excessively long search times.
A significant advance in overcoming these problems has been made with the introduction of the notion of the concept group, which bears certain similarities to the cataloging scheme used in a thesaurus. In the concept group approach, all of the words and phrases in the various languages are divided up among the same limited number of concept groups. Hence, translation consists of identifying the concept group for the word or phrase in the source language, and then searching for its synonym in the same concept group of the target language.
Nevertheless, even the use of the correlated concept groups scheme does not assure a sufficiently compact encoding of the correspondences between the words and phrases of the different languages, nor an optimum search time. There are many small RAM-based translation applications, as well as other applications, such as a PC, where the user desires to dedicate relatively little memory storage to obtain a translation capability, or the user, especially in a hand-held machine environment, needs a fast search capability though constrained by limited processor power.